It seems u can't use host header names while u depoly a SSL website. But each of a DNN multiple websites, which are deployed in one Windows 2003 Server, needs a SSL login&register link for security. How can we work around this contradiction? Does somebody have a good idea?

You can't.  SSL doesn't support host headers.  You need separate web sites on separate IP addresses.  See www.iis.net for help with IIS, it's not realated to DNN at all.  Basically, you install DNN for each SSL site.

That said, if you just need it for login security and have no reason for separate certs for each site, a wildcard cert and parent portals in DNN may work for you.  Wildcat certs are also not DNN, with one you just create the DNN portals as usual.  DNS all points to the same IP.

Jeff

Is Wildcat certs a built-in function in IIS?   I have no idea about it. It seems to be a third-party nonfree software via googleing.